1. Field of the Invention
The present invention relates to an elastic wave device in which an IDT electrode is located on a piezoelectric substrate, and in particular, relates to an elastic wave device that utilizes a piston mode.
2. Description of the Related Art
In the related art, surface acoustic wave devices are known that utilize a so-called piston mode. For example, in Japanese Unexamined Patent Application Publication No. 2011-101350 and Japanese Unexamined Patent Application Publication No. 2013-518455, low acoustic velocity portions are provided on both sides of the center of an IDT electrode in an electrode finger direction, which is a direction in which electrode fingers of the IDT electrode extend, and high acoustic velocity portions are provided on both sides of the low acoustic velocity portions in the electrode finger direction. The low acoustic velocity portions are formed by increasing the width of the electrode fingers or by stacked a mass-adding film, which causes a fall in acceleration, on the electrode fingers. The high acoustic velocity portions are parts where only electrode fingers that are connected to one busbar are arranged in an elastic wave propagation direction. That is, the high acoustic velocity portions are provided outside of an intersection width region in the electrode finger direction. In Japanese Unexamined Patent Application Publication No. 2011-101350, the width, i.e., the dimension in the electrode finger direction, of the high acoustic velocity portions, is at least 1λ and is preferably 3λ or higher.
The intersection width of a surface acoustic wave resonator is at least 10λ, where λ is the wavelength of a surface acoustic wave. As described above, in Japanese Unexamined Patent Application Publication No. 2011-101350, the width of a high acoustic velocity portion is at least 1λ on each side. Therefore, high acoustic velocity portions of such a width have to be provided on both sides of the intersection width region in the electrode finger direction. Therefore, the area of the part of the IDT electrode located inside of the busbars is increased. Therefore, it is difficult to make progress in size reduction.